Recently, an ionomer resin has widely been used as a base resin for an cover of golf balls (e.g. Japanese Patent Publication No. 49-27093). Particularly, the ionomer resin is exclusively used in a two-piece golf ball which is composed of a solid core and a cover covering the solid core. This is because the ionomer resin is good in durability, cut resistance and rebound characteristics and, as well as good processability
However, the ionomer resin is poor in shot feel and control properties (ease of putting spin on the ball) in comparison with a balata (trans-polyisoprene) used as the base resin for the cover of the thread wound golf ball, since the ionomer resin is hard and has high stiffness modulus. Therefore, there has been made intensive study of improving the shot feel and controllability by softening the ionomer resin using various means.
For example, Japanese Laid-Open Patent Publication Nos. 1-308577 and 5-3913 suggest to soften the ionomer resin by blending or mixing it with a special soft ionomer resin obtained by neutralizing a terpolymer of an .alpha.-olefin, an unsaturated carboxylic acid (e.g. acrylic acid, methacrylic acid, etc.) and an acrylate with a sodium or zinc ion.
However, even if the soft ionomer resin as described above is blended, golf balls having shot feel similar to the golf ball having the balata cover have not been obtained. Adversely it raises a problem that the rebound characteristics and flight performance are deteriorated thereby.
Japanese Laid-Open Patent Publication No. 6-192512 suggests use of a mixture of an ionomer resin and a thermoplastic polyamide elastomer, which improves rebound characteristics while maintaining softness. Although the improving effect can also be admitted in view of the maintenance of softness according to this method, rebound characteristic and shot feel are not improved to sufficient range because the softening is conducted by increasing a mixing ratio of the thermoplastic polyamide elastomer.